There has been proposed a multi-layered wiring structure as an approach for achieving a high integration of a semiconductor device. In order to obtain the multi-layered wiring structure, an nth layer and an (n+1)th layer are connected to each other through a conductive layer while thin films called interlayer insulating films are formed in areas other than the conductive layer. Although a SiO2 oxide film has been widely used as a typical interlayer insulating film, there has been a demand to lower a relative dielectric constant of the interlayer insulating film to further accelerate the operation speed of the semiconductor device.
In this regard, an insulating film (referred to as “CF insulating film,” hereinafter) made up of fluorine and carbon (fluorocarbon) has been gaining attention. By using this CF insulating film, the relative dielectric constant can be significantly reduced compared with a silicon oxide film.
Forming of the CF insulating film is carried out, for example, in a plasma processing apparatus, by exciting, e.g., C5F8 which is a source gas of fluorine and carbon and by depositing radicals generated thereby onto a substrate. At this time, a plasma gas used in generating plasma such as argon gas is converted into plasma by, e.g., microwave, and the source gas is excited by this plasma. (e.g., see Japanese Patent Laid-open Application No. H11-162960)
However, as shown in FIG. 10, when forming the CF insulating film, fluorine atoms in the CF insulating film I are arranged at the surface side of the film and exposed at the surface of the film. The fluorine atoms have a high electronegativity and a characteristic of easily adsorbing water molecules. Consequently, if the fluorine atoms are left and exposed at the surface of the film, water molecules will be adsorbed to the fluorine atoms while the substrate is transferred, for example.
Further, when the substrate is heated after the film is formed thereof, for example, the adsorbed water molecules are initiated to react with the fluorine atoms. The fluorine atoms that have been reacted with the water molecules gets released as a hydrogen fluoride gas from the CF insulating film I. Such hydrogen fluoride gas has a property of corroding and destroying the film. For example, the hydrogen fluoride gas may react with a barrier metal film formed between a conductive layer within a semiconductor device and the interlayer insulating film, to destroy and peel off the barrier metal film. This results in an improper multi-layered wiring structure of the semiconductor device, thereby significantly reducing the efficiency of manufacturing the semiconductor device.
Further, the surface of the CF insulating film I may be degenerated by reacting with the water molecules, thereby deteriorating the leak characteristic of the CF insulating film. As a result, the insulating performance of the interlayer insulating film formed by the CF insulating film I decreases, thereby diminishing the performance of the semiconductor device.